As a technology of forming a nanostructure or microstructures on the surface of an object, a technology of forming pores of several hundred nm or less in size using an anodization for a film or substrate comprised of aluminum as a principal component rather than a lithography technology using light rays or electron beams is conventionally known.
The anodization method is a method applying an electric field to a substrate comprised of aluminum as a principal component as an anode in an acid bath oxidation and a dissolution phenomenon and form pores on the surface of the substrate. These pores are formed straightforward in the vertical direction starting from the surface of the substrate, have a high aspect ratio and also have excellent uniformity in diameters of their cross sections. Furthermore, it is possible to control the diameters and spacing of pores by adjusting a current and/or voltage during anodization and control the thickness of an oxide film and depth of pores by controlling the duration of anodization, to a certain extent.
The positions of pores formed using this technique are random, but a technique for obtaining regularly arrayed pore structures is proposed in recent years. This technique forms regularly arrayed concave structures on the surface of a substrate comprised of aluminum as a principal component using an optical lithography and imprint lithography, etc., and conducts anodization using these structures as starting points of pores (U.S. Pat. No. 6,139,713).
There are proposals on various applications focused on a specific geometric structure of this anode alumina and detailed explanations are given by Masuda et al.
Examples of this include an application for a film which takes advantage of wear resistance and insulating properties of an anodized oxide film and an application for a filter with a film peeled off. Attempts are also made using a technology of filling pores with metal, semiconductor or magnetic substance or replica technology of pores for various applications including coloration, magnetic recording medium, EL light-emitting device, electrochromic device, optical device, solar cell, gas sensor, etc. Moreover, a wide variety of applications such as quantum effect devices such as quantum wire and MIM device, molecular sensor using pores as a chemical reaction field, etc., are expected.
A longitudinal recording system, which is the current mainstream of magnetic recording media, becomes more liable to demagnetization as the recording density increases and limitation of its recording density is pointed out. As an alternative technology, there is a proposal on a perpendicular magnetic recording system which records data by magnetizing a recording medium in the vertical (film thickness) direction. According to this system, the demagnetizing field decreases and a more stable state is produced as the recording density increases as opposed to the conventional longitudinal recording system. Furthermore, this system can also increase the thickness of the recording film compared to the longitudinal recording system, and therefore it is said to be resistant to thermal fluctuations in principle. There is a proposal on an application of an anodized oxide film for a perpendicular magnetic recording medium using such a perpendicular magnetic recording system (Japanese Patent Application Laid-Open No. H11-224422).
The above described nano structure is generally formed using a lithography technology and etching technology, but using such techniques, it is extremely difficult to form a high aspect structure which is realized by the anodization method.
Furthermore, the above described magnetic recording medium is disk-shaped and the rotator when information is recorded or reproduced is subject to fine vibration or eccentricity, which prevents recorded tracks from becoming concentric, producing position errors of the head and tracks. Similar position errors are also produced by deformation due to expansion of the disk caused by a thermal distribution in the apparatus. Therefore, the recording area is divided into data areas for recording information and servo areas for detecting track positions and positions are corrected while the head is detecting position information of tracks, but patterned media which are being developed in recent years have a problem as to how to construct servo areas.
The present invention has been implemented in view of the above described problems and it is an object of the present invention to improve the above described points and provide a nano structure having pore array structures in which a plurality of periodic arrays are formed adjacent to one another.
Furthermore, the present invention also provides a method of manufacturing a nano structure in which a plurality of periodic arrays are formed adjacent to one another in a short time by applying anodization to pore starting points formed on a substrate all together at one anodization voltage.
Furthermore, the present invention also provides an optical device with the pores having the nano structure filled with a dielectric having a dielectric constant.
Furthermore, the present invention also provides an optical device with the pores having the nano structure filled with a light-emitting material.
Furthermore, the present invention also provides a magnetic device with the pores having the nano structure filled with a magnetic material.
Furthermore, the present invention also provides a magnetic recording medium capable of constructing effective servo areas by filling pores having the nano structure with magnetic substance and providing a plurality of periodic array structures in the servo areas.